This invention relates to ground fault circuit interrupters, particularly those for personnel protection.
Ground fault circuit interrupters for personnel protection are required in normal practice to be subject to periodic testing to confirm operability. This is implemented by a test circuit branch extending between the hot line conductor on the load side of the sensing transformer of the unit to the neutral conductor on the supply side of the sensing transformer. The test circuit branch comprises a current limiting resistor and also a switch operated by a test button. The test switch is normally open but when the button is depressed and the switch is closed the unit sees a simulated ground fault which should result in a trip and, if not, indicates the device or the manner of its installation is faulty. There is further provided a reset button which is operable after actuation of the test button and the resulting trip to reset the unit to its normal standby condition for operation.
Virani et al. U.S. Pat. No. 4,010,431, Mar. 1, 1977, is representative of a ground fault interrupter, particularly in a receptacle, with provision for a test switch and its operation by a test button and a reset button. The illustrative embodiment shown in the Virani et al. patent is one in which the power contacts operate off a rocking plate (FIG. 6, contact plate 41). In common with other known practice, including those in which the power contacts operate off of a lifting plate, rather than a rocking plate, this device requires separate test and reset buttons for sequentially testing a unit and restoring it to operative condition. All such units are subject to certain defects or drawbacks in their operation. These have to do with the possibility of improper usage of the test and reset buttons that permit what is referred to as "teasing" in which both buttons are simultaneously depressed or are depressed in rapid sequence. Under such conditions it is possible for the unit to be on and conducting to downstream loads while it is disabled from tripping if a ground fault does occur near one of the loads. This is regarded as a highly unlikely combination of circumstances but it may be preferable to have a unit that is not subject to such user abuse and which performs in a trip-free manner at all times. By trip-free is meant the unit will trip any time a ground fault occurs even if the test switch is somehow being manually manipulated in an improper manner.
The present invention achieves the basic purposes of preventing teasing and permitting trip-free operation at all times by unifying the test button and reset button functions, heretofore separately provided, into a unitary mechanism assembly operable by a single manually operable element, such as a push button (referred to herein as a test/reset button or T/R button), that permits initial operation of a test function and then an operation of the reset function only upon completion of the test function. The general construction of this unified test and reset mechanism is one in which a single push button, or other manually operable force applying element, is arranged in a combination with spring elements, contact elements and stop elements so that there are four characteristic positions taken by the mechanism at various stages of operation. In each of the four positions the unit is either on and subject to trip-free operation or is off and immune from the occurrence of a downstream ground fault.
Briefly, the four positions, and their relation to the operative mechanism, are:
A first, latched position, which is the normal standby or operating condition of the unit that permits energization of a load from a supply. The unit is armed for tripping actuation upon occurrence of a ground fault. In the latched position, before any ground fault has occurred, the T/R button is in its normal position which may be generally flush with the surface of the unit and is latched in that position by latch means. Spring means maintain power contacts communicating to the load in a closed position. Test contacts for operation of the test circuit branch are in an open position when the unit is latched.
A second, test position, resulting from a first depression of the T/R button from the latched position which results in the closing of the test contacts while the power contacts remain closed. If the device or its installation are faulty the consequence of moving the button to the test position and releasing it is informative of the defect. The unit returns to the latched position, a trip has not occurred, and the absence of such a trip informs the user that the test was negative. However, in the event of a positive, successful, test, the movement of the T/R button from the latched to the test position causes a ground fault trip signal to be generated and a trip solenoid moves the latch holding the power contacts closing resulting in opening of the power contacts so that the mechanism is now in the third or tripped position.
In the third or tripped position after the release of the latch means, spring elements have caused opening of both the power contacts and the test contacts. The T/R button has moved outwardly to its maximum outward position, though retained in place by a stop means. In its maximum outward tripped position the button indicates to the user that a trip has occurred. This may be by the extent to which the button protrudes from the face of the unit or, preferably, by indicia disposed on a surface of the button such as the side of a pushbutton indicating by a red stripe or other means that only becomes visible upon reaching the tripped position that a trip has occurred.
A fourth, reset position, is one in which the T/R button is again depressed by the user after a trip to a point at which the test contacts again close and are closed upon initially making contact between the power contacts. When the force on the T/R button is withdrawn, the spring means cause outward movement of the elements and the latch means again latches the power contacts closed. The outward movement also releases the test contacts and the unit has returned to the initial latched position for operation.